kate.chem said:

A sustained drop to 1,100 or 1,200 calories reliably under-delivers a predictable set: B12, vitamin D, iron, folate, zinc and magnesium.

Blood count monitoring for micronutrients: my doctor noticed my MCV (mean corpuscular volume) trending up at month 6: 88 → 97 fL. This flagged potential B12 or folate deficiency.

Sure enough, B12 had dropped from 620 to 340 pg/mL. Started B12 injections monthly and MCV normalized within 2 months. GLP-1 agonists can impair B12 absorption — this is a real clinical concern that deserves routine monitoring.

Following on from LindaRN_retired — and this may be the naive question:

Was that from a primary source or from a summary of one?

bri_stats said:

Blood count monitoring for micronutrients: my doctor noticed my MCV (mean corpuscular volume) trending up at month 6: 88 → 97 fL.

Adding the part of the answer the thread has not reached. It is worth asking what the claim would look like if it were false. If nothing would look different, it is not a claim about the world and no amount of discussion will settle it.

OP back with an update, since a thread like this is useless without one.

Closing the loop. The answer turned out to depend on the detail I had left out of the opening post, which is a lesson about how to ask rather than about the subject.

PedsEndoPhilly said:

It is worth asking what the claim would look like if it were false.

That is right for the common case. Whether it is right for the case being asked about depends on a detail that has not been given.